The Antigenicity of Ultra-Violet Irradiated Vaccinia Virus

Abstract

Summary Vaccinia virus which has been inactivated by exposure to ultra-violet irradiation under strictly controlled conditions produces an immunity response in rabbits and monkeys. This can be measured by relative insusceptibility to challenge with living virus and by the titration of circulating antibody. Experiments with small doses of living virus in excess of those that might have been given accidentally indicate that the immune response to the irradiated material was not due to traces of living virus that had escaped detection. There is a logarithmic relationship between exposure to irradiation and destruction of virus. The exposure necessary to produce complete inactivation can be deduced from a knowledge of this relationship. Excessive exposure destroys the antigenicity of the preparations. The antigenicity of irradiated virus can be preserved for at least 6 months at 4°C. and at least 2 months at 37°C. by drying from the frozen state. Circulating antibody is detectable in rabbits for at least 22 weeks following immunization, and a single subsequent reinforcing dose is followed by a secondary immune response. The possibility that preliminary immunization with irradiated virus may diminish the risk of complications and reduce the severity of the reaction to subsequent Jennerian vaccination with living virus is discussed. This material may provide a basal immunity in those individuals in which vaccination is contraindicated.